The present disclosure relates to a duplex stainless steel sheet, and more particularly, to a method for manufacturing a duplex stainless steel sheet having reduced inclusions through a twin roll strip casting process.
In general, a twin roll strip casting process refers to a process of directly and continuously producing a steel strip having a thickness of several millimeters (mm) from molten steel supplied between a pair of rotating casting rolls. Referring to FIG. 1, a twin roll strip caster 100 for twin roll strip casting generally includes casting rolls 110, a ladle 120, a tundish 130, a casting nozzle 140, a meniscus shield 150, brush rolls 160, and edge dams 170.
In a twin roll strip casting process, molten steel is supplied to the ladle 120, and the molten steel flows to the tundish 130 through a nozzle. Then, the molten steel is supplied from the tundish 130 to a region among the casting rolls 110 and the edge dams 170 attached to both ends of the casting rolls 110 through the casting nozzle 140, and the molten steel starts to solidify in the region. At this time, the meniscus shield 150 protects the surface of the molten steel solidifying in the region between the casting rolls 110 so as to prevent oxidation, and an appropriate gas is supplied to control the atmosphere of the region. In this state, while the molten steel solidifies, the molten steel is drawn from the region through a gap between the casting rolls 110 as a strip 180.
In such a twin roll strip casting process for directly producing a strip having a thickness of 10 mm or less, some techniques may be necessary to produce a strip having no cracks and a desired thickness at a high production rate by supplying molten steel through the casting nozzle 140 to the region between the casting rolls 110 rotating in opposite directions at high speed. However, fine inclusions may be formed in duplex stainless steel steels produced using the twin roll strip caster 100 because rapid solidification of molten steel does not allow for a sufficient time for inclusions to grow and combine with each other.
Such inclusions remaining on the surfaces of products may lead to surface damage or cracks and may act as sites lowering corrosion resistance. Particularly, non-metallic inclusions are inevitably formed during processes such as a molten steel deoxidizing process or a ferroalloy supplying process for temperature control. That is, although the formation of inclusions is inevitable, it is necessary to reduce or minimize the formation of inclusions.